/// <summary>
        /// Computes a shortest paths tree from the specified sourceVertex to every other vertex in the edge-weighted directed graph
        /// </summary>
        /// <param name="graph">The edge-weighted directed graph</param>
        /// <param name="sourceVertex">The source vertex to compute the shortest paths tree from</param>
        /// <exception cref="ArgumentOutOfRangeException">Throws an ArgumentOutOfRangeException if an edge weight is negative</exception>
        /// <exception cref="ArgumentNullException">Thrown if EdgeWeightedDigraph is null</exception>
        public DijkstraShortestPath(EdgeWeightedDigraph graph, int sourceVertex)
        {
            if (graph == null)
            {
                throw new ArgumentNullException("graph", "EdgeWeightedDigraph cannot be null");
            }

            foreach (DirectedEdge edge in graph.Edges())
            {
                if (edge.Weight < 0)
                {
                    throw new ArgumentOutOfRangeException(string.Format("Edge: '{0}' has negative weight", edge));
                }
            }

            _distanceTo = new double[graph.NumberOfVertices];
            _edgeTo     = new DirectedEdge[graph.NumberOfVertices];
            for (int v = 0; v < graph.NumberOfVertices; v++)
            {
                _distanceTo[v] = Double.PositiveInfinity;
            }
            _distanceTo[sourceVertex] = 0.0;

            _priorityQueue = new IndexMinPriorityQueue <double>(graph.NumberOfVertices);
            _priorityQueue.Insert(sourceVertex, _distanceTo[sourceVertex]);
            while (!_priorityQueue.IsEmpty())
            {
                int v = _priorityQueue.DeleteMin();
                foreach (DirectedEdge edge in graph.Adjacent(v))
                {
                    Relax(edge);
                }
            }
        }
        private DijkstraShortestPath(EdgeWeightedDigraph graph, int sourceVertex, int?destinationVertex)
        {
            if (graph == null)
            {
                throw new ArgumentNullException(nameof(graph), "EdgeWeightedDigraph cannot be null");
            }

            foreach (DirectedEdge edge in graph.Edges())
            {
                if (edge.Weight < 0)
                {
                    throw new ArgumentOutOfRangeException($"Edge: '{edge}' has negative weight");
                }
            }

            _distanceTo = new double[graph.NumberOfVertices];
            _edgeTo     = new DirectedEdge[graph.NumberOfVertices];
            for (int v = 0; v < graph.NumberOfVertices; v++)
            {
                _distanceTo[v] = double.PositiveInfinity;
            }
            _distanceTo[sourceVertex] = 0.0;

            _priorityQueue = new IndexMinPriorityQueue <double>(graph.NumberOfVertices);
            _priorityQueue.Insert(sourceVertex, _distanceTo[sourceVertex]);
            while (!_priorityQueue.IsEmpty())
            {
                int v = _priorityQueue.DeleteMin();

                if (destinationVertex.HasValue && v == destinationVertex.Value)
                {
                    return;
                }

                foreach (DirectedEdge edge in graph.Adjacent(v))
                {
                    Relax(edge);
                }
            }
        }